1. Field of the Invention
The present invention relates to digital control of lighting devices, and more particularly to digital control of large lighting systems, including systems having multi-parameter light fixtures, with multiple communications systems.
2. Description of Related Art
Multi-parameter light fixtures, which include light fixtures having individually remotely adjustable beam size, color, shape, angle, and other light characteristics, are widely used in the lighting industry because they facilitate significant reductions in overall lighting system size and permit dynamic changes to the final lighting effect. Applications and events in which multi-parameter light fixtures are used to great advantage include showrooms, television lighting, stage lighting, architectural lighting, live concerts, and theme parks.
In practice, the multi-parameter light fixtures of a system are typically controlled by a central controller. Prior to the advent of relatively small commercial digital computers, remote control of light fixtures from a central controller was done with either a high voltage or low voltage current; see, e.g., U.S. Pat. No. 3,706,914, issued Dec. 19, 1972 to Van Buren, and U.S. Pat. No. 3,898,643, issued Aug. 5, 1975 to Ettlinger. With the widespread use of computers, digital serial communications was widely adopted as a way to achieve remote control; see, e.g., U.S. Pat. No. 4,095,139, issued Jun. 13, 1978 to Symonds et al., and U.S. Pat. No. 4,697,227, issued Sep. 29, 1987 to Callahan.
Digital communications between the central controller and the multi-parameter light fixtures typically is by wire. In 1986, the United States Institute of Theatre Technology ("USITT") developed a digital communications system protocol for multi-parameter light fixtures known as DMX512. While the DMX512 protocol has been updated several times since its adoption, the basic communications protocol remains the same. Basically, the DMX512 protocol consists of a stream of data which is communicated one-way from the control device to the light fixture using an Electronics Industry Association ("EIA") standard for multipoint communications know as RS-485. FIG. 1 shows an illustrative system based on the USITT DMX512 protocol. Power mains 12 provide AC power to a central controller 10 and light fixtures 20, 22, 24, 26, 32, 34 and 36 over standard building electrical wiring 14. A communications cable 16 is run from the central controller 10 to the first multi-parameter light fixture 20, and additional communication cable segments 21, 23, 25, 31, 33 and 35 sequentially connect the light fixtures 22, 24, 26, 32, 34 and 36. While only seven multi-parameter light fixtures are shown in FIG. 1 for clarity, typically multi-parameter lighting systems may have thirty or more such light fixtures. Communication is in a single direction, as shown by arrows adjacent the communications cable 16 and cable segments 21, 23, 25, 31, 33 and 35. From time to time, light fixtures must be placed in locations which are hard to reach or otherwise present difficulties during installation and cabling. A hard to reach or difficult area 30 containing light fixtures 32, 34 and 36 is included in FIG. 1.
An illustrative light fixture 100 suitable for use in the multi-parameter lighting system of FIG. 1 is shown in greater detail in FIGS. 2 and 3. The front view of FIG. 2 shows a light housing 110 which is rotatably attached to a yoke 108. The yoke 108 is in turn rotatably attached to an electronics module 104, which contains a power supply and communications and control electronic circuits. A panel area 106 on the electronics module 104 contains a display and various buttons for manually setting the operating address of the light fixture 100. The side view of FIG. 3 shows that the electronics module 104 also includes a pair of digital communications terminals, one of which is a digital input terminal 112 designated DIGITAL LINE IN and the other of which is a digital output terminal 114 designated DIGITAL LINE OUT. Internally, the input terminal 112 typically is looped through to the output terminal 114. Respective communications cables plug into the terminals 112 and 114. A line cord 102 for connecting the multi-parameter light fixture 100 to the power line extends from the electronics module 104. Illustrative multi-parameter light devices are described in the product brochure entitled The High End Systems Product Line 1996 and are available from High End Systems, Inc. of Austin, Tex.
To maintain reliability throughout the multi-parameter lighting system, the communications cables typically are dedicated metallic or fiber optic cables. One reason is the central controller for the multi-parameter light fixtures of a system may be a considerable distance from the light fixtures. For example, central controllers may be located over one hundred meters from the light fixtures they control in such places as large arenas, theaters, and auditoriums. Lengthy cable runs are also found in commercial buildings in which light fixtures are used for architectural lighting, since the communications cables must pass from floor to floor or between widely separated rooms on the same floor. Moreover, a typical large lighting system contains over thirty light fixtures and a corresponding number of communications cables between the light fixtures, and requires significant labor to connect securely each of the light fixtures and the central controller to the power mains and their respective communications cables. Installation of multi-parameter lighting systems tend to be quite costly, taking into consideration the individual costs of the cables, the associated connectors, and the labor involved in installing them.
During the transition from analogue control to digital control, some multi-parameter light fixtures were constructed with both a digital and an analog means of communication. An example of such a device is the TrackSpot.RTM. automated luminaire, which is described in the product brochure entitled The High End Systems Product Line 1996 and is available from High End Systems Inc. of Austin, Tex. The TrackSpot system has a wide variety of control options, including digital and analog. The analog communication is designed as an input, and the device is manually selectable between the digital and analog input schemes. The analog communication to the device controls the device that it is connected to, whereas the digital communications "loops through" from light to light with an addressable signal scheme for controlling multiple addressed light fixtures.
The TrackSpot fixture is physically switched on the fixture to assume either a master or a slave position. With the fixture set to the master position, an analog signal at the analog input to the fixture causes the master to execute a particular one of numerous memory resident programs based on the analog value it receives. The master also sends a digital signal to the other fixtures that are set up as "slaves" to cause them to act on their respective memory resident programs.
Despite advances in the control of large lighting systems, a need exists for improving the digital control of large systems that include multi-parameter light fixtures.